NUT (Network UPS Tools) is a
collection of programs that provide a common interface for monitoring
and administering UPS hardware. It uses a layered approach to connect
all of the parts.

Drivers are provided for a wide assortment of equipment. They
understand the specific language of each UPS and map it back to a
compatibility layer. This means both an expensive smart protocol
UPS and a simple power strip model can be handled transparently.

This information is cached by the network server upsd, which then
answers queries from the clients. upsd contains a number of access
control features to limit the abilities of the clients. Only authorized
hosts may monitor or control your UPS hardware if you wish. Since the
notion of monitoring over the network is built into the software, you
can hang many systems off one large UPS and they will all shut down
together.

Clients such as upsmon(8) check on the status of
the hardware and do things when necessary. The most important task is
shutting down the operating system cleanly before the UPS runs out of
power. Other programs are also provided to log UPS status regularly,
monitor status through your web browser, and more.

NUT includes also CGI clients that run through your web server. They
allow you to see UPS status and perform certain administrative commands
from any web browser. Javascript and cookies are not required. The CGI
programs use a configuration file, hosts.conf, to see if
they are allowed to talk to a host. This keeps malicious visitors from
creating queries from your web server to random hosts on the Internet.

Some SGI-specific files have been added to this distribution,
specifically the /etc/init.d startup scripts and
/usr/freeware/etc/nut/nut-apache.conf.sample, a sample
Apache config file.